202 Proceedings of Royal Society of Edinburgh, [march 5 , 
"Valentin (Purkinje and Valentin, Physiologic) arrived at the 
same results. The observations and conclusions of this paper, 
referring solely to Mytilus ed.ulis, may he summarised as follows : — 
1st. Entire animal removed from the shell moves ; the movement 
is rotatory; it rotates at an average rate of 15 minutes per round, 
and it retained power of movement for 21 hours in one case, and 
50 J hours in another. 
2nd. Detached mantle-lobes, gills, labial palps, and foot, either 
entire or in parts, also move. 
3rd. Mantle-lobes rotate in the direction of attached margin, 
posterior end acting as pivot ; the rate of rotation is 4J hours per 
round ; the rate of currents on muscular margin is fully 2 inches per 
minute. 
4th. Gills have a composite movement, consisting of translation 
and simultaneous rotation ; they rotate in the direction of detached 
margin, usually on posterior end as a pivot; they travel in the 
direction of the cut surface, either horizontally, vertically, or upside 
down ; the horizontal rate of movement is 2 minutes per inch, or 
44 days per mile ; the vertical rate is 7 minutes per inch ; and the 
upside down rate is 2J minutes per inch ; rate of current on free 
margin is J minute per inch or 2 inches per minute ; similar to that 
on muscular margin of mantle-lobe. 
5th. Labial palps have various movements, but principally 
rotatory; the inner rotate inward normally, and the outer rotate out- 
ward ; the inner and outer of same side rotate in opposite directions ; 
the rate of rotation of inner is 2J minutes per round, and of outer 
3 minutes; rotation may occur either on base or tip; graceful 
gliding translatory movement on surface or margin at the rate of 
1 inch in 2J minutes; also turning over from one surface to the 
other in succession; duration of movement for 7 days. 
6th. Foot has both a translatory and rotatory movement, usually 
the former ; rate of rotation, nearly 7 hours per round ; average rate 
of translation, 1 inch per hour, or 7 years per mile ; duration of 
movement for 3 days at least ; direction of translatory movement 
always away from the cut surface. 
7th. Labial palps act as guards and not guides to the mouth, 
since the direction of their ciliary currents is always away from the 
mouth on the margin continuous with the lips. 
